Centrifugal pumps work by using an impeller to increase the pressure and flow of a liquid. Liquid enters the center of the impeller and is accelerated outward by the curved blades of the impeller. This increases the pressure and flow of the liquid. Calculating the required head of a centrifugal pump involves accounting for static head, pipe friction losses, and adding additional head for safety. Proper pump selection is based on matching the required head and flow rate to the pump performance curves. Cavitation and ensuring adequate Net Positive Suction Head (NPSH) are also important considerations for centrifugal pump operation.

1. Centrifugal Pumps

2. What To Expect?
Head Power
Efficiency Applications Tidbits
Videos

3. Positive
Displacement
Centrifugal
Types
Of
Pumps

4. • Centrifugal Pump Working
• Liquid enters through a suction connection
concentric with the axis of a high speed
rotary element called the impeller, which
carries radial vanes integrally cast in it.
Liquid flows outward, and leaves the
impeller at a considerably greater with
respect to the ground than at the entrance
to the impeller.
• Power is applied to the fluid by the
impeller and is transmitted to the impeller
by the torque of the drive shaft which
usually is driven by a direct connected
motor at constant revolutions commonly at
1750 r/min.

5. A Centrifugal Pump

7. Centrifugal Pumps
• Increase of mechanical energy, pressure
by centrifugal force…
• Most commonly used in the industry…
• The impellers are curved backward…

10. Let’s Start!
Head

12. 1
P
S D
Reservoir
Shut Off Head 50 feet
*In accordance with pump curves

13. In certain systems (admittedly unusual), the pump
discharge line may have to run at a much higher elevation
than the final discharge point. The fluid must first reach
the higher elevation in the system. If the shut-off head is
smaller than the static head corresponding to the high
point, then flow will not be established in the system.
During start-up and checkout of the pump, a quick way to
determine if the pump has the potential capacity to
deliver the head and flow required, is to measure the
shut-off head. This value can be compared to the shut-off
head predicted by the performance curve of the pump.

14. Total Head is proportional to the difference in
pressure at the discharge vs. the suction of the
pump.
To obtain a higher head, the rotational speed or
the impeller diameter can be increased.

15. • So to calculate your head you need the
following...
1. Flow rate in GPM or m^3/hour...
2. Friction losses...
We are going to be using the flowrate of
20 GPM with 50 feet of total NOT VERTICAL
pipe.
[PD-PS/ꝭ]= height(2-1) + Friction Losses(2-1)
Head

16. • How To Choose A Pump
• Usually we choose a pump on the basis of it’s head which
is basically a generic term given to the total
mechanical energy content of a fluid at a given point in
a piping system. So once we have established the no. of
feet and flow rate that we want we want we can go to the
manufacturer.
1
Pump
2
S D
Reservoir
Tank
Flow Rate 7GPM
.5 inch
15 feet

18. • The table does not know how many feet of
pipe you have so therefore it lists
pressure loss for a 100 feet of pipe.
100 feet of pipe
48.8 feet of head loss We have 50 feet of pipe =24 feet

20. Height from point 1 to point 2, in our case it is
15ft…
1. You also need to account for the head you’re
going to be losing because of the friction and
you need to accommodate that, you can
calculate the lost head due to friction by the
use of tables, here you need to know the
nominal diameter of your pipe and flow rate in
gal/min…… Now all you have to do is add them
up…
• Also you ought to add a factor of 15-20 % for
a commercial design to the values of the
table...
(Head) = 15ft + 24ft = 39ft

21. Characteristic Curves
• The performance of a given pump is
commonly illustrated by plots of
actual head, power consumption, and
efficiency versus volumetric flow
rate. These plots are called
characteristic curves.
• ΔH is head capacity
• P is power of the pump
• Ƞ is the pump efficiency
• NPSHR

23. 1. Technically if the head and the flow rate
operating point for your system is located
above on or below a performance curve then
that pump will be sufficient to do it’s job
(but do remember the economics!)...
2. A fixed speed circulator forces the system to
work on it’s curve, a variable speed
circulator adjusts its curve to meet the needs
of the system.

24. Product
Name
Pump Curves
This Means that at flow
of 12 GPM in the
product 007-(5) the
pump will create a head
of 6.4 ft. Or at 4 feet
of head the pump will
generate a flowrate of
17 GPM.
12
6.4
17
4

25. • Pump Head Compensation
• From an industrial point of view pump head is very
important, for every elbow/bend in pipe you have to add
in a certain no. of head usually in feet in order to
accommodate the losses… i.e. 1elbow=2feet then you’d
have to add in 2 feet for every time that elbow appears
in the piping…
• So, you can see here the elbows are causing us 2 feet
loss in head every time they appear so we have to add
that in order to compensate the losses… We also have 3
ft. loss in head due to the vertical piping, we don’t
count in horizontal piping…
• So, Total Head = 9ft. + 12ft. + some excess feet to be
safe...
Pump
Tank
22
2
22
2
3
3
3

26. • Cavitations And NPSH
• If the suction pressure is only slightly
greater than the vapor pressure some liquid may
flash to vapor inside the pump a process called
as cavitations which greatly reduces the pump
capacity and causes severe erosion. If the
suction pressure is actually less than the
vapor pressure there will be vaporization in
the suction line and no liquid can be drawn
into the pump.
• To avoid the cavitations the pressure at pump
inlet must exceed the vapor pressure by a
certain value called as the net positive
suction head. The required value of NPSH is
about 2 to 3 m (5 to 10 ft) for small
centrifugal pumps but It increases to 15m (50
ft) are recommended for larger pumps.

28. Tid Bits

29. Rotary Pumps
Multi Stage Centrifugal Pumps
• High energy centrifugal can generate a head of 200 m only.
• To increase the head (>200 m), multistage centrifugal pumps is used
where multiple impeller is installed on a single shaft.

30. Imp. Dia.
90
1000
60
800
15
Efficiency (82%)

31. Pump Priming
• What is it?
• To remove the entrapped air inside the pump is
called pump priming
• When we do it?
1.First start up after a long time
2.First start up after maintenance
3.First start up for a new pump
• How we do it?
• If there is any air entrapped in the suction line, we
need to replace this air with liquid.
• Air can be displaced by pouring liquid from any tank
into the suction line and submerge the pump impeller…
Positive displacement pump can compress the gas to a
required discharge pressure, that’s why they are known to
self priming…

32. Pump Priming
Priming of a pump is very essential step in start up of
a centrifugal pump.
Fact is that centrifugal pump are not capable of
pumping air or vapors.
Priming is the process in which the impeller of a
centrifugal pump will get fully sub merged in liquid
without any air trap inside. This is especially
required when there is a first start up. But it is
advisable to start the pump only after primping.
Liquid and slurry pumps can lose prime and this will
require the pump to be primed by adding liquid to the
pump and inlet pipes to get the pump started. Loss of
"prime" is usually due to ingestion of air into the
pump. The clearances and displacement ratios in pumps
used for liquids and other more viscous fluids cannot
displace the air due to its lower density.

33. • Cavitations And NPSH
• If the suction pressure is only slightly
greater than the vapor pressure some liquid may
flash to vapor inside the pump a process called
as cavitations which greatly reduces the pump
capacity and causes severe erosion. If the
suction pressure is actually less than the
vapor pressure there will be vaporization in
the suction line and no liquid can be drawn
into the pump.
• To avoid the cavitations the pressure at pump
inlet must exceed the vapor pressure by a
certain value called as the net positive
suction head. The required value of NPSH is
about 2 to 3 m (5 to 10 ft) for small
centrifugal pumps but It increases to 15m (50
ft) are recommended for larger pumps.

34. Pump Safety
A note about centrifugal pump is that it doesn’t require a
safety valve while a P.D pump must have a safety valve
because at certain pressure C.F pump will stop producing
any further pressure while the P.D pump will continue to
increase pressure with every stroke until or unless the
Safety valve blows or the discharge is opened…
Turbulence
Turbulence may be generated in other ways than by
flowing fluid in a pipe… in general however it
results from either of these scenarios, one is
the flowing fluid gets In contact with a solid
boundary called as the wall turbulence or two
fluid layers moving with varying velocities
contact called as the free turbulence… Free
turbulence is especially important in mixing…